Transcript Deserts - yr8geography

Deserts
Intro Flash vid to Jack Johnson music
http://blip.tv/scripts/flash/blipplayer.swf?autoStart=false&file=http://blip.tv/file/get/Adtastic2001-Deserts994.flv?source=3
• Deserts occur where evaporation is greater than
precipitation or where precipitation is less than 250
millimetres a year
• These areas cover about 30% of the earth’s surface.
• Some of the worlds deserts are hot and others are cold
• All, however are dry.
COLD
HOT
Types of Desert
• The world’s deserts are often classified according to the
amount of precipitation they receive.
Classification
Extremely
Arid
Arid
Semi Arid
Amount of Precipitation
No Precipitation for 12
consecutive months
Less than 250 millimetres of
precipitation per year
Between 250 millimetres and 500
millimetres of precipitation per
year
Hot Deserts
• Hot deserts generally lie around
the tropic of cancer or the
tropic of Capricorn.
• They have very hot summers
and warm winters.
• Temperature extremes are
common, as cloud cover is rare
and humidity is very low.
• This means there is nothing to
block the heat of the sun during
the day or prevent its loss at
night.
• Temperatures can range
between around 45° and -15 °
Celcius in a 24 hour period.
Cold Deserts
•Cold Deserts lie on high ground
generally north of the Tropic of
Cancer and south of the tropic of
Capricorn.
•They include the polar deserts
•Any precipitation falls as snow
•Winters are very cold and often
windy; summers are dry and mild
to warm.
24 Deserts Game http://www.purposegames.com/game/111
Where are deserts located?
• Cold ocean currents exist off the Western
sides of continents. Winds blowing over
these currents lose their moisture over the
sea and are dry by the time they get to
land.
• In the interior of continents
• Winds blowing over continents are dry by
the time they get to the interior of
continents.
Location of Deserts
• Depressions/basins in the interior of
continents
• The surrounding highlands around
depressions/basins cause a rainshadow
effect leaving the depression dry.
Location of Deserts
• The leeward side of tall mountains
• Moisture carrying winds are blocked by the
side (windward side) of tall mountains. The
other side (leeward side) is consequently
dry, and deserts may be formed there.
Account for the location of deserts?
1. Cold ocean currents off the west coast of
continents
2. Dominance of high pressure systems
3. Lack of relief rainfall
Cold ocean currents
There are cold ocean currents off the west
coast of most continental landmasses.
Evaporation rates from cold water are low.
This limits the amount of moisture in the
air and the amount of precipitation.
Deserts & winds
Dominance of high
pressure systems
Deserts & winds
1) Deserts: where & why
Deserts & winds
Deserts: where & why
Australia
• Apart from Antarctica, Australia is the
driest continent in the world. About 35% of
the continent receives so little rain, it is
effectively desert. In total, 70% of the
mainland receives less than 500mm of
rain annually, which classes it as arid, or
semi-arid.
Flash of atmospheric circ http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=12426&ResourceID=40425
Australia's deserts, listed below, are distributed throughout
the western plateau and interior lowlands. The total desert
area equates to 18% of the total mainland area of Australia.
Deserts & winds
Lack of relief rainfall
Middle-latitude deserts
 exist in rain shadows.
Orographic Rainfall
The air mass, now
drier, flows down
the leeward side of
the mountains
The air mass is
forced to rise as it
hits the mountain
and condenses
into clouds
Warm moist air
approaches a
mountain barrier
The dry air mass becomes warmer, with little
chance of rain. Deserts are often found on the
leeward side of large mountain ranges
Orographic
rainfall occurs
on the
windward side
of the
mountains
Orographic Rainfall
The air mass, now
drier, flows down
the leeward side of
the mountains
The air mass is
forced to rise as it
hits the mountain
and condenses
into clouds
Warm moist air
approaches a
mountain barrier
The dry air mass becomes warmer, with little
chance of rain. Deserts are often found on the
leeward side of large mountain ranges
Orographic
rainfall occurs
on the
windward side
of the
mountains
Climate (Atmosphere and
Hydrosphere)
• The desert temperature is not always hot.
During the night, desert temperatures are
quite cold, even below freezing point. The
daytime temperatures are hot because
there is very little cloud cover. This means
that maximum radiation from the sun
reaches the surface of the earth. In
summer the temperature can reach as
high as 40°C, while in winter, the
temperature can reach 24°C.
Large diurnal range
• At night time, the lack of cloud cover
allows the heat of the day to escape
quickly, resulting in cold, even freezing,
temperatures. The difference between the
daily minimum and maximum
temperatures is known as the diurnal
range.
Desert Landforms
• A plateau is a broad, level, elevated region
commonly bounded partly by cliffs.
• A mesa is smaller, flat-topped hill bounded by
cliffs. They are usually wider than they are high.
• A butte is a narrow hill of resistant rock bounded
by cliffs. Buttes are usually higher than they are
wide.
• A wadi is steep sided, flat floored desert
watercourse (river or creek) which is usually dry.
•
Alluvial Fans are fan-shaped deposits of material in
zone of deposition. They form where water flowing down
wadis meets the desert and dumps its sediment.
• Playa Lakes are ephemeral (temporary) lakes where
water flows into a desert depression. Eventually the
water evaporates and salt pans or clay pans are formed.
• Inselberg is an isolated hill of harder rock.
• A Bolson is the flat desert basin.
A sandy desert or an
erg surface
A stony desert or an
reg surface
(known as a gibber plain in Australia)
A rocky desert or
hamada surface
Using pg 255 of the text draw and
Annotate and label
All 4 sand dunes in figure 12.2e
Use the heading Sand Dunes.
Then read p254 and describe the
4 types of dunes
Transverse dunes
Reg or stony desert
Erg or sandy desert
Inselbergs
Barchan dune
Star dunes
Alluvial fan
Arch
Animation http://www.classzone.com/books/earth_science/terc/content/visualizations/es1601/es1601page01.cfm?chapter_no=visualization
Butte
Badlands
Desert Landforms
• http://www.youtube.com/watch?v=m35i4B
7Lfl4 Top Gear in Botswana 10 mins
•
•
•
•
Examine the following 5 photographs
What have these pictures got in common?
Divide them into two types of landscape.
Which is the odd one out?
Photo 1 – Monumental hills
Photo 2
The
mountains
above a
stream
Photo 3 – sand and sky
Photo 4 – “Badlands landscape”
Photo 5 The archway
The photos and the questions
• Monumental hills
• The mountains above
a stream
• Sand and sky
• “Badlands” landscape
• The archway
• 1 What have they all
got in common?
• 2 Which is the odd
one out? [and why]
• 3 If you had to put
them into 2 groups –
which ones would you
put together ?
Explain.
Here is what one pupil thought!
They all look rather mountainous
with exposed rock and very steep
slopes.
I put these three together – I
think!
These photos seemed to form
another group
They both have flat areas which are kind of bumpy – but
not seriously mountainous like the others?
This was the odd one out!
• This was the odd
one out because it
had water in running
and that would have
eroded the
landscape in a
different way to all
the others!
• Do you agree
with the pupil’s
opinions?
Processes affecting landform
shapes:
• Erosion:
• Erosion is the picking up and removal of
material. Erosion occurs as a result of the
action of wind, water, ice, waves and
gravity.
Weathering:
• Weathering is the breaking down of
materials (rock and soil) into smaller
materials through the action of weather
such as temperature changes, rainfall and
wind.
Deposition:
• Deposition is the accumulation of
sediment by the action of agents such as
water and wind. Water can deposit
sediment to build landforms such as
alluvial fans: wind can deposit sediment,
such as sand, to build sand dunes.
Interactive game 2 players
• http://www.games4geog.com/cg/desertintr
o.swf
Desert
Keyword Quiz
10 Questions
1
Name the landform
What type of desert is Mr Anderson in?
2
3
Name the landform
4
Name the landform
5
Name the landform
6
Name the landform
7
Name the landform
8
What type of desert is this?
9
Name the landform
10
Name the landform
Desert
Keyword Quiz
10 ANSWERS
1
Name the landform
wadi
What type of desert is Mr Anderson in?
2
erg
3
Name the landform
alluvial fan
4
Name the landform
mesa
5
Name the landform
sand dune
6
Name the landform
butte
7
Name the landform
escarpment
8
What type of desert is this?
reg
9
Name the landform
oasis
10
Name the landform
playa
DESERT
ANIMALS
Fat reserves stored for when
food is scarce
Animal Facts- Animal Survivors
• Because of the lack of vegetation, there are very few
food chains in deserts.
Able to carry large amounts
• Most desert animals are small,
which
keeps
heat
of water
(equal
to about
25%
its body
its
gain and loss to a minimum. of
They
areweight
alsoinmostly
stomach
CAMEL
nocturnal.
sweat in
glands,
so theyor under
be by No
• Most Nostrils
avoid that
thecan
heat
hiding
burrows
don’t lose water through
closed during sand
rocksstorms
by day and beingperspiration.
active during the night or
early morning.
Small to
Collects dry seed,
• Some
desert
which
it stuffsanimals
into its also have adaptations for keep heat
gain and
cheeks. It empties
conserving
water.the
loss at a
seeds into its burrow,
• Insects
reptiles
have thick outer coverings minimum
so
where and
they soak
up
thatwater
they
loseexhaled
little water as possible through
vapour
in the rats breath.
evaporation.
KANGAROO RAT
When it eats the seed it
get its water back.
Camels
• The camel originally came from Asia where it
was domesticated and then introduced into
Africa. It has been used there by nomadic tribes
such as the Tuareg in their camel caravans,
carrying goods such as dates, salt and millet.
Camels have a large number of adaptations
allowing them to survive in the desert. Many of
these adaptations can be seen in these
photographs.
Camel Adaptations
• Wide spreading feet to prevent the camel
from sinking into the sand
• Tough patches of skin on their knees for
kneeling
• Thick fur to insulate them from the sun
• The hump, used for storing fatty tissue
(not water), to provide energy
Adaptations
• Tough lips for eating hard, thorny plants
• Long eyelashes, hairy ears and nostrils that
close to keep sand and dust out
• Camels can also go for days without drinking
water.
• They can smell water, which can be quite a
number of kilometres away
• They can drink salty water
• They can drink up to 100 litres (or 1⁄3 of their
body weight) in 10 minutes and then travel for
100 kilometres on this supply.
• Desert plants are called xerophytes. They
have adapted to the harsh climatic
conditions of low and irregular rainfall,
extreme temperatures and high
evaporation by being able to store water or
reduce moisture loss through
transpiration so that they can survive.
DESERT
PLANTS
Plant survivors
• Drought resistant plants are known as xerophytes
• Many of these plants are known as succulents,
which means they are able to store water in their
tissues.
• Most desert plants have small leaves that are spiky
or wax coated. This reduces transpiration and deters
animals.
• Some send their roots deep into the ground to tap
into the ground water table.
• They spread their shallow roots to increase their
personal catchment area for when it rains, and are
widely spread to avoid competition for water.
• Many plants are ephemerals, which means they can
complete their full life cycle in just 2 – 3 weeks
taking advantage of any rain that falls.
Photosynthesis
takes place in the
green stem (the
cactus has no
leaves)
Thick cell walls
that do not break
when they dry out
A thick, waxy coating
keeps the water inside
the cactus from
evaporating.
Instead of leaves,
most cacti have
spines or scales
(which are
modified leaves).
These spines and
scales do not lose
water through
evaporation
(unlike regular
leaves, which lose
a lot of water).
The spines
protect the cactus
from predators
(animals that
would like to eat
the cactus to
obtain food and/or
water)
Plant adaptations: Desert plants differ in the ways they adapt themselves to the hot and
dry environment.
Some desert plants have a short life cycle. When the rains come, these plants sprout
quickly, flower and die. Their seeds lie dormant in the soil, until the next rain enables them
to germinate and bloom.
Most desert plants grow far apart and their roots extend out so that each plant can get
water and minerals from a large area. Other desert plants have roots that extend deep into
the ground to obtain water from deep beneath the ground.
When it rains, cactuses and other succulent (juicy) plants take up as much water as
possible and store it in their leaves and stems which will provide the water they need during
the dry months. Their waxy leaves and stems also slow down water loss through
transpiration. Other plants survive by shedding their leaves in dry periods to reduce water
loss.
Animal adaptations: Desert animals include many kinds of insects, spiders, reptiles,
birds and mammals. They are adapted to the heat as well as scarcity of water.
Deer, foxes, wolves and other animals may visit a desert after a rainfall in search of food.
Butterflies and bees emerge from their pupa state to feed on the flowers that bloom. The
insects breed quickly so that the next generation reaches the pupa stage before the desert
dries up.
Many small animals hide under rocks or dig burrows underground and stay there during the
day to escape the heat and the sun. Most desert animals are nocturnal - they avoid the
extreme midday heat by feeding at night, when the temperature has dropped and the air is
much cooler. Some of them are dormant (inactive) in the summer.
Larger desert animals try to stay in shady areas during the day. They obtain water from the
food they eat and from the few water holes that exist in a desert. The camel stores its food
as fat in large humps on its back. The stored fats are broken down to help the camel
survives long periods without food and water.
Deserts Multiple Choice Quiz
• file:///G:/28%20April%202008%20Thumbst
ick/8%20Geography/12.Deserts/SOSE%2
0Alive%20Geography%201.mht Now in
keep but not use file
Desertification Intro flash player
• http://www.sln.org.uk/geography/magicsto
nes/Default.htm play both parts 1 and 2.
• About causes and magic stone solutions.
Going To Extremes: Hot
• http://news.nationalgeographic.com/news/
2004/02/0227_040227_TVhot.html Dallol,
in northern Ethiopia's Danakil Depression.
• http://www.smh.com.au/news/world/awalk-through-the-desert-in-the-shoes-ofthepeople/2008/05/02/1209235156062.html?
page=fullpage#contentSwap2 2008 SMH
article on Afar